I guess they meant to stipulate that it's sunny-16 conditions outside, which means they're basically asking "how many stops difference between f/2.8 at 1/50 and f/16 at 1/800?" Seems like a reasonable exercise for someone learning to do calculations in stops, though it's not expressed in the clearest way (which could be down to the asker or the original exercise).

-NT

Nathan Tenny
San Diego, CA, USA

The lady of the house has to be a pretty swell sort of person to put up with the annoyance of a photographer.
-The Little Technical Library, _Developing, Printing, And Enlarging_